Overcurrent-protective snap switches provide immediate protection against overcurrent damage when the electrical motor is blocked in household apparatus such as vacuum cleaners in that the switches automatically interrupt the supply of current to the motor and the normal operating condition is reestablished only after the switches are manually reset.
German Pat. No. 1,513,242 discloses an overcurrent-protective snap switch wherein two movable contact arms are arranged in parallel. On the one hand, the ends of these two parallel arms are disposed in a two-part mounting bracket and the free-swinging end carries a contact. The thin center tongue is electrically connected to a terminal point; however, the center tongue is only held in a form-tight manner. The contact end transmits the electrical energy to the second connecting point via a contact with the aid of spring pressure. The thin center tongue thereby defines an electrical resistance element which expands in correspondence to the value of current exceeding the rated current and permits the free contact to snap out of its first end position thereby separating the contact pieces to interrupt the current. A manually actuable reset device is provided to reset the snap switch.
The above solution has the disadvantage however that when such overcurrent-protective snap switches are utilized in a floor-cleaning apparatus, the thin center tongue is often electrically and mechanically destroyed since the normal area of application for safety devices of this kind is for electronic devices such as hi-fi amplifiers and the like. It can be assumed on a statistical average that a floor-cleaning device is completely blocked at least once a week because of an object drawn in by suction when, for example, a carpet is vacuum cleaned. Even carpet tassels at the edge of the carpet can cause such a blockage when drawn into the vacuum cleaner by suction. The resulting current load from this blockage is then approximately 2.5 amperes at 220 volts for approximately 52 switching operations in a year. Because of the center tongue which is necessarily thin and which brings about the snap-switching action of the contacts and the electrical load, the arc does not always jump with certainty to the contacts provided during the switching operation; instead, the arc jumps to the forward region of the thin center tongue which then is subjected to a welding action. Further, the center tongue is then so intensely damaged that with the next "normal" switching operation, the thin metal segment mechanically breaks at this location.